Influenza is the seventh leading cause of death in the United States (Beigel J H (2008), Crit Care Med 36(9):2660-2666). The elderly, the very young, pregnant women and otherwise immune-compromised populations account for over 90% of influenza-related deaths. The pandemic H1N1 influenza virus strain is immunologically distinct from other influenza viruses, leaving large population groups susceptible to infection (Brockwell-Staats et al., Influenza Other Respi Viruses 3:207-21, 2009; Dawood et al., N Engl J Med 360:2605-2615, 2009; Garten et al., Science 325:197-201, 2009; Hancock K, et al. (2009) N Engl J Med 361(20):1945-1952). The Center for Disease Control (CDC) reports that the 2009 H1N1 pandemic strain caused an estimated 60 million cases and 256,000 hospitalizations. An unusually high frequency of severe disease occurred in younger and otherwise healthy patients (Hancock et al., 2009, supra). In addition, rare infections with avian H5N1 influenza strains in humans had close to a 50% mortality rate (Subbarao and Joseph, 2007, Nat Rev Immunol 7:267-278). Emergence of a zoonotic or antigenically distinct strain that combined even a fraction of the morbidity and mortality of the pandemic H1N1 and H5N1 viruses would have dire consequences.
Antibodies play a key role in protection against influenza infection in vivo (Gerhard et al., 1997; Immunological reviews 159:95-103; Luke et al., 2006, Annals of internal medicine 145:599-609; Puck et al., 1980, Journal of infectious diseases 142:844-849; Simmons et al., 2007, PloS Medicine 4:e178). The fact that there was little or no pre-existing antibody titers present prior to the emergence of this pandemic virus, and that the virus atypically caused such severe disease in young adults illustrates the importance of comprehensively understanding the B cell responses and antibody specificities induced by infection with this influenza virus. A need remains for reagents to treat and diagnose an influenza virus infection in a subject.